Noble Corp (NE.N) exercised options with Sembcorp Marine (SCMN.SI) to build two new harsh-environment shallow water drilling rigs for US$235 million ($296.9 million) apiece, bringing the total it has under construction to four, the company said on Monday. The new jack-up rigs are expected to be delivered by Sembcorp's Jurong Shipyard in the third quarter of 2013 and first quarter of 2014, and still leave Noble with two options to build new jack-ups. The vessels will have the capability to operate in water depths up to 400 feet (122 meters) and drill to depths of 30,000 feet. Earlier this month, Noble said it had landed contracts for six shallow-water rigs off the coast of Mexico, including four that had been idled in the U.S. Gulf of Mexico because of the lack of work. ...